II. Abstract: Autoimmunity is a self-destructive immune disorder and often directed towards a particular tissue or organ. Although the disease manifestations can be tissue-specific, they do not necessarily originate in that particular tissue. Furthermore, individuals with a specific autoimmune disease are at risk to develop additional autoimmunity directed towards other target tissues. What all autoimmune diseases do have in common is that they result from a breakdown in self-tolerance, with a major contribution from pathogenic self-reactive T cells. T cell tolerance towards self is initially established in the thymus during the process of thymic selection. Strong self-reactive T cells are either clonally deleted or alternatively clonally deviated to become regulatory T cells that are key suppressors of auto-aggressive immune cells. Since this decisive selection process plays a fundamental role in self-tolerance, we postulate that susceptibility to autoimmunity might originate from a principal defect in the central process that governs clonal deletion versus clonal deviation. The proposal will test this hypothesis and ultimately seek to identify the primary deficiency and contributing factors that underlie susceptibility to autoimmunity. Understanding the defect(s) is this selection process will ultimately allow for early detection of individuals that are at a high risk to develop autoimmune diseases. Aside from detecting autoimmune susceptibility, this research will have vital implications for the prevention and effective treatment of autoimmune diseases. Although it is feasible to induce the production of suppressive regulatory T cells through immunization with selfantigens, it is possible that pathogenic self-reactive cells will be generated, thus exacerbating the disease. Our proposed study will explore a novel strategy to prevent and/or treat autoimmunity. Hepatic stellate cells will be used as natural, regulatory, antigen-presenting cells to assure the efficient generation of regulatory T cells that may suppress pathogenic autoimmune cells and thereby control autoimmunity.